Department of Mathematics, University of Arizona,
Tucson, Arizona 85721.
We would like to thank the following for their valuable contributions :
David O. Lomen Bill McCallum.
We also acknowledge the support of the National Science Foundation.
This program may be freely distributed by any means, including bulletin
boards, provided that there is no fee or charge or consideration of any
kind which is in excess of $8. However, we retain all the rights to this